Heavy metal trout

Posted on October 05, 2015

We are well aware that pollution in its many guises is typically bad news for trout: nutrient enrichment causing increased oxygen demands; fine sediments blocking up spawning gravels; or contaminants wiping out food supplies are just a few of the more ​‘obvious’ contenders. But now there is evidence of something even more insidious impacting upon the very blueprint of trout.

WTT friends at the University of Exeter have found that historic mining activities in south west England has led to a reduction in genetic diversity of brown trout and indicating that human activity can alter the genetic patterns of wild populations at an alarming rate.

To investigate the genetic impacts of metal pollution, the research team compared DNA samples from fifteen brown trout populations from heavily-polluted and relatively uncontaminated rivers. Their analysis revealed that trout from metal polluted rivers derived from a single common ancestor during the medieval period (~950 years ago) when tin mining in the region was first documented.

Further genetic separation appears to have occurred when rivers were again polluted with increased concentrations of metals during the Industrial Revolution (~150 years ago).

So, while some trout have evolved to live in water contaminated with metals, their genetic diversity is low and populations are small. Furthermore, despite being geographically close, even the metal-tolerant populations are genetically distinct from each other and thus it looks like they have evolved to cope with specific ​‘cocktails’ of metals in rivers too.